1. Field of the Invention
The present invention relates to a process for producing a bumper made of a synthetic resin for an automobile vehicle, and particularly, to an improvement in a process for producing a bumper made of a synthetic resin for an automobile vehicle and having a sandwich structure comprised of a core and an outer layer covering the core, the process including a first step of injecting an outer layer forming material into a bumper forming cavity through a gate in a mold, and a second step of injecting a core forming material to allow the core forming material to flow into the outer layer forming material existing in the gate and the cavity and to allow the outer layer and core forming materials to flow within the cavity.
2. Description of the Related Art
In the prior art, such a bumper includes a bumper main portion extending laterally from a central portion of a vehicle body, and a pair of bumper sides connected to opposite ends of the bumper main portion, and has a substantially uniform thickness in its entirety.
Therefore, the cavity in the mold includes a main area for forming the bumper main portion, and a pair of side areas for forming the pair of bumper sides, and has a uniform distance in its entirety for compliance with the thickness of the bumper. The gate opens, for example, into a section of the cavity for forming an upper portion of the bumper main portion in the main area.
In such a producing process, while the outer layer forming material is flowing within the cavity, the core forming material is allowed to flow into the outer layer forming material. However, after the outer layer forming material is filled into the cavity to stop its flowing, it is difficult to allow the core forming material to further flow into the outer layer forming material.
If the distance of the cavity is set substantially constant under such a situation as in the prior art, the following problem is encountered: a large difference is produced between the time taken for the outer layer forming material injected into the cavity at the first step to be filled in the main area into which the gate opens, and the time taken for such outer layer forming material to be filled in each of the side areas spaced apart from the gate. Due to this, it is difficult to produce a bumper having a sandwich structure in its entirety.